Noisy environments may be uncomfortable and distracting, so it may be desirable to reduce the impact of unwanted noise from such environments. For example, in a passenger vehicle, it would be beneficial to minimize unwanted noises, such as road noise, in the vehicle's cabin to increase the comfort level for the passengers.
Noise cancellation systems may be used to reduce such unwanted noise (also referred to as “target noise”) from an environment by generating a substantially contemporaneous cancellation noise having the same amplitude and frequency as the unwanted noise, but 180 degrees out-of-phase. As a consequence, when the sound waves of the two noises meet at a particular location, the two noises substantially cancel one another by destructive interference, which allows occupants of the environment to perceive less unwanted noise.
Noise cancellation systems, however, may fail for a variety of reasons. When failure occurs, the noise cancellation system may have no effect on the target noise and worse, may increase the amount of noise in the environment.
As disclosed in U.S. Pat. No. 5,809,152 (“the '152 patent) issued to Nakamura et al. on Sep. 15, 1998, an adaptive noise suppression system may be automatically disengaged when the system detects the amount of noise in a space is increasing. Specifically, the '152 patent discloses a noise suppression system including a phase and amplitude control device for determining a secondary sound for reducing noise in the space, microphones for detecting remaining noises in the noise space, a divergence prediction device for judging whether the secondary sounds are normal or are moving to an abnormal state, and a control stop device for preventing the output of the secondary sound. Based on predictions made by the divergence prediction device, the control stop device may automatically disengage the noise suppression system before a noise increase occurs.
The divergence prediction device disclosed by the '152 patent predicts whether the noise suppression system is diverging based on an error signal provided from noise in the space detected by the microphones. However, because the error signal includes whatever noises are received by the microphones, any unusual noises occurring in the space affect the accuracy of the divergence prediction device's determination. Accordingly, the divergence prediction device may disengage the noise suppression system when unusual noises occur in the space rather than, for example, due to the divergence of the system. In addition, because the noise suppression system disclosed by the '152 patent only predicts divergence, the system does not consider other potential failure states that may affect the system and, therefore, cannot implement other remedial measures corresponding to the different failure states.
The disclosed methods and systems for noise cancellation are directed to overcoming one or more of the problems set forth above.